This invention relates to pumps for pumping fluids and in particular liquids and control systems for such pumps. The invention will be described in relation to a lubrication system for an internal combustion engine, although it is to be appreciated that other applications are also envisaged.
It is important in lubrication systems of internal combustion engines that oil is delivered at appropriate rates to the various moving surfaces and components of the engine. This is especially important for crankcase scavenged two stroke internal combustion engines. In such engines, oil is consumed during the operation of the engine and is typically not completely recirculated as in conventional four stroke engines. Therefore, the rates of oil delivery must be carefully controlled to ensure minimal resultant exhaust gas emissions, prevent contamination of any catalytic device of the engine due to excess oil in the exhaust gases and to extend the period between oil refills.
Generally, the required rate of oil delivery varies widely depending on the engine, the load and speed operating point of the engine, the previous operating history of the engine and various other operating conditions. For example, for some two stroke cycle engines, the fuel/oil ratios can typically vary between 400:1 in low load and idle conditions, and 80:1 in sustained high load conditions. These conditions are typically determined by various sensors and a control system may control the rate of oil delivery from the pump. The control system may be external from or integral with the pump itself.
The rate of oil delivery from the pump can however also be affected by factors such as the viscosity of the oil and the voltage provided by the battery supplying power for the operation of the pump. Higher than normal oil viscosities and below normal battery voltages can result in lower than expected oil delivery rates from the pump. Other factors which would typically affect the oil delivery rate include blockages within the oil supply and/or delivery lines, air trapped within the oil system, or depletion of the oil supply. Furthermore, the transient changes to the engine operating conditions such as going from a long period of operation at a low load and speed to a higher load and speed operating point may affect the oiling rate in that a delayed increase in oiling rate may be desirable to account for any oil which may have accumulated in the engine during the previous period of operation. It has not however previously been possible to conveniently control the pump such that the above noted factors can be taken into account to ensure correct and consistent oil or fluid delivery rates.
It is an object of the present invention to provide a pump control system which takes into account at least one of the above factors.